FORM AND STRUCTURE OF MUSCLES. 



13 



called skeleton muscles. These muscles occur in various 

 forms. Sometimes they are flat, thin bands, and some- 

 times cylindrical cords, some of which are of considerable 

 length. Others again are thicker in the middle than at 

 the ends ; in these cases the middle is called the trunk, 

 the ends are spoken of as the head and tail, of the muscle. 

 Some muscles have two or more heads — that is, two or 

 more ends — springing from different points on the bone, 



a 



^33.33C!.^XXX3 



d 



Fig. 4. Stkiatkd musclk-fibrks. 



fl. Two fibres cut tlirough in tlio middle, and passing, on the left, into tendons, b. A 

 single muscle-fibre deprived of its discs, and separating into fibrilliE. c Two 

 single fibrilljB. d. A muscle-fibre separating into its discs. 



and uniting in a common trunk. But these muscles, 

 whatever their external shape, always consist of several 

 fibres, united into a bundle, and together forming the 

 muscle as a whole. One of these fibres, when isolated, 

 will be found to be very minute, and scarcely visible to 

 the naked eye ; when seen, enlarged from 250 to 300 

 times, under the microscoj)e, it appears as a pouch, 

 consisting of a firm, solid wall, with certain contents ; 

 and this contained matter exhibits alternate lighter and 



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